This invention relates to remote control systems for television receivers and more specifically to remote control systems having a charge storage means and means for sampling the charge to effect a control function.
Remote control systems for television receivers typically include a remote ultrasonic transmitter for transmitting a plurality of ultrasonic signals of different frequencies and an ultrasonic receiver. The ultrasonic receiver typically includes a plurality of frequency discriminators or detectors each for detecting one of the plurality of transmitted signals. A control function is associated with each of the ultrasonic detectors and is initiated upon receipt of the corresponding signal. While prior are remote control systems typically included bi-directional motors mechanically coupled to a potentiometer or similar device, and such systems utilizing motors are still advantageously used in some applications, a preferred form of remote control system includes a circuit which stores a charge and provides a direct control voltage to a variable gain amplifier or the like. One such system is disclosed in U.S. Pat. No. 3,637,922 issued to G. K. Srivastava wherein first and second resonant circuits provide output signals to fire a neon bulb which charges and discharges, respectively, a memory capacitor. The charge on the memory capacitor is sampled by a field-effect transistor to provide a direct control voltge to control a phase shift circuit used as a tint control in a color television receiver. The direct control voltage can also be used to control other functions as well as tint. Also, it is known to use a relay circuit to charge and discharge the memory capacitor instead of a neon bulb.
In order for a television receiver to be fully controlled by a remote transmitter, it is necessary for the remote control system to be powered at all times including times when the television receiver is off so that the television receiver can be turned on by the remote transmitter. It has been found, however, that in one prior art arrangement when the television receiver was off for an extended period, the charge on the memory capacitor undesirably changed in a direction to drive the field-effect transistor far beyond cut-off so that a remote transmission of a substantial length of time was required to return the charge on the memory capacitor to the proper operating point. For example, in a circuit to control the volume and on/off functions, a substantial length of time was required to turn the television receiver on. It was further found that the cause of the undesired discharging of the memory capacitor was extraneous ultrasonic noise which energized the remote control receiver to fire the neon bulb or close the relay momentarily. Such momentary charging periods when repeated over a period of time caused a substantial undesired discharging of the memory capacitor.
In other instances an operator may inadvertently or in some cases intentionally continue the remote transmission beyond the time necessary to accomplish the desired function. For example, where the volume and on/off functions are combined, a remote transmission that decreases the volume until the television receiver turns off may be continued so that the memory capacitor associated with those functions becomes undesirably charged requiring an excessively long transmission to turn the television receiver on again.